Fluorenylidene-acridan derivative, method for producing the same, mechanochromic material, charge transport material, and electronic device

Abstract

To provide a fluolenylidene-acridan derivative that has excellent property.SOLUTION: Provided is a compound that is represented by 9-(3,6-dimethyl-9H-fluorene-9-yliden)-10-phenyl-9,10-dihydroacridine, 9-(3,6-difluoro-9H-fluorene-9-yliden)-10-phenyl-9,10-dihydroacridine, 9-(3,6-dimethoxy-9H-fluorene-9-fluorene)-10-phenyl-9,10-dihydroacridine, 9-(2,7-dibromo-9H-fluorene-9-ylidene)-10-phenyl-9,10-dihydroacridine, 9-(2,7-thiophene-9H-fluorene-9-yliden)-10-phenyl-9,10-dihydroacridine, and 9-(2,7-dinitro-9H-fluorene-9-ylidene)-10-phenyl-9,10-dihydroacridine.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to fluorenylidene-acridan derivatives, mechanochromic materials comprising the fluorenylidene-acridan derivatives, charge transport materials, and electronic devices. [Background technology]

[0002] Materials that change color in response to external mechanical stimuli such as pressing are called mechanochromic materials, and have attracted attention as new functional materials that can be applied to sensors, switches, etc. The present inventors have succeeded in synthesizing a substance that changes its absorption color significantly in response to mechanical stimuli (see Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] "A fluorenylidene-acridane that becomes dark in color upon grinding. Ground state mechanochromism by conformational change," Chem. Sci., 2018, Vol. 9, pp. 475-482 Summary of the Invention [Problem to be solved by the invention]

[0004] The present inventors have continued their research into materials with even higher properties and have arrived at the present invention.

[0005] The present disclosure has been made in view of the above problems, and an object of the disclosure is to provide a fluorenylidene-acridan derivative having excellent properties. [Means for solving the problem]

[0006] In order to solve the above problems, one embodiment of the present disclosure is a fluorenylidene-acridan derivative. The fluorenylidene-acridan derivative is represented by the following formula (1): [ka] (where R 1 ~R 16 At least one of R is an organic group, and the rest are hydrogen atoms or organic groups. 17 is a hydrogen atom or an organic group.

[0007] Another aspect of the present disclosure is a method for producing the above-mentioned fluorenylidene-acridan derivative, which comprises the steps of introducing an organic group into acridone or fluorene, and producing the fluorenylidene-acridan derivative of formula (1) by a cross-coupling reaction of acridone and fluorene.

[0008] Yet another aspect of the present disclosure is a mechanochromic material comprising the fluorenylidene-acridan derivative described above.

[0009] Yet another aspect of the present disclosure is a charge transport material comprising the fluorenylidene-acridan derivatives described above.

[0010] Yet another aspect of the present disclosure is an electronic device comprising the above-described mechanochromic material or the above-described charge transport material. Effect of the Invention

[0011] According to the present disclosure, it is possible to provide a fluorenylidene-acridan derivative having excellent properties. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram showing the molecular structure of a fluorenylidene-acridan. [Diagram 2] FIG. 1 shows a synthesis scheme for fluorenylidene-acridan derivatives 5a to 5f of Examples 1 to 6. [Diagram 3] FIG. 2 shows the UV spectrum of a fluorenylidene-acridan derivative of an example. [Figure 4] FIG. 1 shows various chromisms of fluorenylidene-acridan derivatives. [Diagram 5] FIG. 1 shows UV spectra of fluorenylidene-acridan derivatives. [Figure 6] FIG. 1 illustrates the protonation of fluorenylidene-acridan derivatives. [Figure 7] FIG. 1 shows free energy diagrams of fluorenylidene-acridan derivatives. [Figure 8] FIG. 1 shows the single crystal X-ray structure of a fluorenylidene-acridan derivative. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] FIG. 1 shows a schematic diagram of the molecular structure of fluorenylidene-acridan. Fluorenylidene-acridan (9-(9H-fluoren-9-ylidene)-9,10-dihydroacridine) cannot take a planar structure as a whole molecule due to interference between hydrogen atoms at opposing positions of the fluorene and acridan moieties, and takes a molecular structure distorted out of plane. FIG. 1(a) shows a bent conformation, and FIG. 1(b) shows a twisted conformation. The bent fluorenylidene-acridan shown in FIG. 1(a) is yellow, and the twisted fluorenylidene-acridan shown in FIG. 1(b) is dark green. The dark green color of the twisted type is due to charge transfer absorption from the acridan moiety, which has electron donor properties, to the fluorene moiety, which has electron acceptor properties.

[0014] Fluorenylidene-acridans usually exist in a bent form in a solid, but change to a twisted form when subjected to an external mechanical stimulus. This causes the solid, which was yellow, to turn dark green. The fluorenylidene-acridans that have changed to the twisted form return to their original bent form when exposed to solvent vapor or heated. The change between the bent form and the twisted form is reversible, and can be repeated many times. As will be described later, it has been found that not only the color but also the electrical properties differ between the bent form and the twisted form. Therefore, by utilizing such reversible changes in color and electrical properties, fluorenylidene-acridans can be applied to sensors for detecting pressure and stress, switches that can be turned on and off by pressing, touch panels that change color when pressed, copying paper, educational toys, memo pads, and the like. In addition, by utilizing the charge transfer absorption with a high extinction coefficient, they can be applied to electronic devices such as solar cells.

[0015] In such applications, in order to adjust the color, absorbance, and electrical properties before application of a mechanical stimulus, the color, absorbance, and electrical properties after application of a mechanical stimulus, the degree of mechanical stimulus required for the change between the bent and twisted forms, and the like, the present inventors have synthesized fluorenylidene-acridan derivatives by introducing various substituents into the fluorene moiety or acridan moiety of fluorenylidene-acridan and evaluated their properties.

[0016] The fluorenylidene-acridan derivatives of the present disclosure have the following structure: [ka] Here, R 1 ~R 16 At least one of R is an organic group, and the rest are hydrogen atoms or organic groups. 17 is a hydrogen atom or an organic group.

[0017] The organic group may be, for example, an alkyl group, a heteroalkyl group, an alkenyl group, a heteroalkenyl group, an alkynyl group, a heteroalkynyl group, a cycloalkyl group, a heterocycloalkyl group, an aryl group, a heteroaryl group, an alkoxy group, a carbonyl group, a carboxy group, a cyano group, a hydroxy group, a thiol group, an amino group, an imino group, a nitro group, a halogen, or a combination thereof.

[0018] R 17 may be an aromatic ring group that is unsubstituted or has one or more substituents. The aromatic ring may be, for example, a benzene ring, a condensed ring such as naphthalene, anthracene, phenanthrene, or pyrene, or a heterocyclic ring such as furan, thiophene, pyrrole, pyrazole, imidazole, pyridine, pyridazine, pyrimidine, or pyrazine. The aromatic ring may have any substituent such as an alkyl group, a heteroalkyl group, an alkenyl group, a heteroalkenyl group, an alkynyl group, a heteroalkynyl group, a cycloalkyl group, a heterocycloalkyl group, an aryl group, a heteroaryl group, an alkoxy group, a carbonyl group, a carboxy group, a cyano group, a hydroxyl group, a thiol group, an amino group, an imino group, a nitro group, or a halogen, or may have no substituent.

[0019] In the above-mentioned applications, in order to change the color and electrical properties of only the pressed area and to clearly distinguish it from the non-pressed area, it is preferable to have a molecular structure that makes the bent type more stable than the twisted type. The twisted type has zwitterionic properties due to partial charge transfer from the acridan moiety, which has properties as an electron donor, to the fluorene moiety, which has properties as an electron acceptor, and it is considered that dipole-dipole interactions contribute to stabilization. Therefore, it is considered that the stability of the twisted type can be relatively lowered and the stability of the bent type can be relatively increased by weakening the charge transfer from the acridan moiety to the fluorene moiety by introducing an electron-withdrawing group into the acridan moiety or an electron-donating group into the fluorene moiety and lowering the zwitterionic property of the fluorenylidene-acridan derivative. Therefore, R 1 ~R 8At least one of R may be an electron donating group such as an amino group, a hydroxy group, or an alkoxy group. 9 ~R 17 At least one of R may be an electron-withdrawing group such as a carbonyl group, a carboxyl group, a nitro group, or a halogen. 1 ~R 17 Depending on the type and number of substituents introduced into R, the twisted structure may be more stable than the bent structure. 1 ~R 8 or R 9 ~R 17 The stability of the twisted form may be further increased by introducing an electron donating group into at least one of the fluorene moieties or acridan moieties. In order to adjust the color, absorbance, and electrical properties before the application of a mechanical stimulus, the color, absorbance, and electrical properties after the application of a mechanical stimulus, and the level of mechanical stimulus required for the change between the bent form and the twisted form, the type, number, and position of the electron donating or electron withdrawing group introduced into the fluorene moiety or the acridan moiety may be designed.

[0020] 2 shows a scheme for synthesizing the fluorenylidene-acridan derivatives 5a to 5f of Examples 1 to 6. The fluorenylidene-acridan derivative of formula (1) can be produced, for example, by a step of introducing an organic group into acridone or fluorene, and a step of producing the fluorenylidene-acridan derivative of formula (1) by a cross-coupling reaction of acridone and fluorene. The step of producing the fluorenylidene-acridan derivative may include a step of converting acridone to thioacridone, a step of diazotizing fluorene, and a step of producing the fluorenylidene-acridan derivative of formula (1) by a reaction of thioacridone with diazofluorene.

[0021] The step of introducing an organic group into acridone or fluorene may be carried out by selecting an appropriate synthesis method depending on the type, number, position, etc. of the organic group to be introduced.

[0022] The step of converting the acridone to a thioacridone may include, for example, converting the carbonyl group to a thiocarbonyl group by treating the unsubstituted or substituted acridone with Lawesson's reagent (2,4-bis(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane-2,4-disulfide). This step may be carried out by refluxing the acridone and Lawesson's reagent in a solvent such as tetrahydrofuran (THF).

[0023] The step of diazotizing fluorene may include the steps of reacting fluorene with hydrazine to generate fluorenone hydrazone, and oxidizing the fluorenone hydrazone to generate diazofluorene. The step of generating fluorenone hydrazone may be carried out by refluxing fluorene and hydrazine in a solvent such as ethanol. The step of generating diazofluorene may be carried out by oxidizing fluorenone hydrazone with silver(I) oxide in a solvent such as ethanol or dichloromethane containing potassium hydroxide.

[0024] The cross-coupling reaction of thioacridones and diazofluorenes may be carried out via the Barton-Kellogg reaction.

[0025] The mechanochromic material of the present disclosure includes a fluorenylidene-acridan derivative having a structure of formula (1), which provides a mechanochromic material with excellent properties.

[0026] The charge transport material of the present disclosure includes a fluorenylidene-acridan derivative having a structure of formula (1), which provides a charge transport material with excellent properties.

[0027] The electronic device of the present disclosure includes the above-mentioned mechanochromic material or the above-mentioned charge transport material. The electronic device may be, for example, an organic semiconductor, an organic solar cell, or the like. This makes it possible to provide an electronic device with excellent characteristics.

[0028] [General Procedures for Examples 1 to 6] 10-Phenylacridine-9(10H)-thione (compound 4, 1 equivalent) and triphenylphosphine (1 equivalent) were placed in a Schlenk bottle and sealed with a rubber stopper. The reaction system was designed to be kept under nitrogen atmosphere at normal pressure by using a Schlenk line. To start the reaction, 4 mL / mmol of anhydrous xylene was injected into the bottle, and diazofluorene (compound 3, 1 equivalent) was added using a dropping funnel. The mixture was refluxed for 1 hour. After removing the solvent by vacuum distillation, the mixture was charged into a silica gel short column and impurities were removed through dichloromethane. The product was then eluted from the silica gel through a triethylamine / dichloromethane mixed solvent (1 / 1 to 1 / 5), and a dark green or blue compound was collected. A second stage of silica gel column chromatography pretreated with triethylamine was performed using petroleum ether / dichloromethane (10 / 1) as the eluent, and the target compound 5 was obtained in a yield of 35.70%.

[0029] [Example 1: Synthesis of 9-(3,6-dimethyl-9H-fluoren-9-ylidene)-10-phenyl-9,10-dihydroacridine (5a)] Following the procedure described above, the phenylthioacridan (287.0 mg, 1.0 mmol) was reacted with the diazofluorene 3a (236.0 mg, 1.0 mmol). After two rounds of chromatography and removal of the solvent, a dark blue solid 5a was obtained in 53% isolated yield (222.3 mg).

[0030] [Example 2: Synthesis of 9-(3,6-difluoro-9H-fluoren-9-ylidene)-10-phenyl-9,10-dihydroacridine (5b)] Following the procedure described above, the phenylthioacridan (287.0 mg, 1.0 mmol) was reacted with the diazofluorene 3b (228.0 mg, 1.0 mmol). After two rounds of chromatography and removal of the solvent, a dark blue solid 5a was obtained in 57% isolated yield (253.3 mg).

[0031] [Example 3: Synthesis of 9-(3,6-dimethoxy-9H-fluoren-9-ylidene)-10-phenyl-9,10-dihydroacridine (5c)] Following the procedure described above, the phenylthioacridan (287.0 mg, 1.0 mmol) was reacted with the diazofluorene 3c (252.3 mg, 1.0 mmol). After two rounds of chromatography and removal of the solvent, a dark blue solid 5c was obtained in 64% isolated yield (306.5 mg).

[0032] [Example 4: Synthesis of 9-(2,7-dibromo-9H-fluoren-9-ylidene)-10-phenyl-9,10-dihydroacridine (5d)] Following the procedure described above, the phenylthioacridan (287.1 mg, 1.0 mmol) was reacted with the diazofluorene 3d (350.0 mg, 1.0 mmol). Two rounds of chromatography and removal of the solvent afforded a dark blue solid 5d in 51% isolated yield (294.5 mg).

[0033] [Example 5: Synthesis of 9-(2,7-thiophene-9H-fluoren-9-ylidene)-10-phenyl-9,10-dihydroacridine (5e)] Following the procedure described above, the phenylthioacridan (287.1 mg, 1.0 mmol) was reacted with the diazofluorene 3e (356.5 mg, 1.0 mmol). After two rounds of chromatography and removal of the solvent, a dark blue solid 5e was obtained in 58% isolated yield (338.2 mg).

[0034] [Example 6: Synthesis of 9-(2,7-dinitro-9H-fluoren-9-ylidene)-10-phenyl-9,10-dihydroacridine (5f)] Following the procedure described above, the phenylthioacridan (287.1 mg, 1.0 mmol) was reacted with the diazofluorene 3f (282.2 mg, 1.0 mmol). After two rounds of chromatography and removal of the solvent, a dark blue solid 5f was obtained in 47% isolated yield (239.2 mg).

[0035] [Crystal structure] The crystal structures of the fluorenylidene-acridan derivatives 5a to 5e were analyzed by single crystal X-ray diffraction. 5b and 5c were bent crystals, and 5d was a twisted crystal. The bent and twisted structures coexisted in 5a and 5e, and in particular, 5a contained both the bent and twisted structures in one unit cell. Good crystals could not be obtained for 5f.

[0036] [UV-Visible absorption spectrum] Figure 3 shows the UV spectra of the fluorenylidene-acridan derivatives of the examples. Figure 3(a) shows the temperature change of the UV spectrum of 5a in DMF, Figure 3(b) shows the temperature change of the UV spectrum of 5b in DMF, Figure 3(c) shows the temperature change of the UV spectrum of 5c in DMF, Figure 3(d) shows the temperature change of the UV spectrum of 5e in DMF, Figure 3(e) shows the van't Hoff plot of 5e, Figure 3(f) shows the Gaussian curve fitting of the UV spectrum of 5e, and Figure 3(g) shows a conceptual diagram of the equilibrium between the twisted and bent forms.

[0037] The absorption band around 430 nm contains both the twisted and bent conformations. To analyze the contribution of each conformation to this absorption, the temperature change of the UV-Vis absorption spectrum was measured. As shown in Figure 3(a)-(d), when the temperature was increased from 30°C to 110°C, the absorption around 680 nm decreased due to the decrease in the twisted conformation. However, in the short wavelength region, both a decrease and an increase were observed, indicating that both conformations contribute to the absorption in this region.

[0038] When the temperature was increased, the equilibrium shifted from the staggered form to the bent form. Le Châtelier's principle showed that this change in equilibrium from the staggered form to the bent form was an endothermic reaction. The solution was cooled from 110°C to 30°C to check the reversibility of the spectrum, and the spectrum was the same as before heating.

[0039] The UV-Vis absorption spectrum of 5e has less overlapping absorption in the short wavelength region than other compounds, allowing for clearer analysis. With increasing temperature, the spectrum of 5e showed an increase in the intensity of three peaks (around 680 nm, 360 nm, and 310 nm) and a decrease in the intensity of one peak (430 nm). Based on the UV-Vis absorption spectrum of the solid, the color of the single crystal of the staggered form, and the results of DFT calculations of 5e, the absorption band around 680 nm was assigned to the staggered form. In addition, according to the law of conservation of mass, the three absorption bands around 310 nm, 360 nm, and 430 nm were assigned to the staggered form, staggered form, and bent form, respectively.

[0040] The proportion of the absorption of the bent form in the absorption of 5e around 430 nm was calculated using Gaussian curve fitting, and it was found to be 92.5%, which was almost entirely due to the bent form. Therefore, the equilibrium between the twisted form and the bent form of 5e was investigated based on the absorption around 430 nm in the ultraviolet-visible absorption spectrum. By formulating simultaneous equations based on the law of conservation of mass and the Beer-Lambert law and substituting the measured molar absorption coefficient, etc., the abundance ratio of the bent form to the twisted form at 30°C (i.e., the equilibrium constant) was calculated to be 3.86. In other words, it can be seen that the bent form is significantly more dominant than the twisted form. The reason why the color of the inferior twisted form is sometimes observed is because the extinction coefficient of the twisted form is larger than that of the bent form.

[0041] A van't Hoff plot was constructed to calculate the changes in enthalpy, entropy, and Gibbs free energy. The change in enthalpy was calculated to be ΔH = 4.21 kJ / mol, indicating that the change from the staggered form to the folded form is endothermic. The change in free energy was calculated to be ΔG = -3.43 kJ / mol, indicating that the folded form is more stable, which is consistent with the calculated equilibrium constant. The change in entropy was very small, ΔS = 0.0252 kJ / mol, indicating that this change is an intramolecular change involving only a conformational transformation.

[0042] [Chromism] In the solid state, 5a, 5c, and 5e are predominantly bent, which allows them to exhibit various types of chromism (reversible color change upon external stimuli). Experiments of mechanochromism, thermochromism, solvatochromism, vapochromism, and proton-induced chromism were carried out.

[0043] Figure 4 shows various chromisms of fluorenylidene-acridan derivatives: (a) mechanochromism, (b) vapochromism from green to yellow by DCM vapor, (c) thermochromism and DSC curves at 70 °C, (d) color change induced by dissolution in DCM and UV spectrum in solid state, (e) shows 5a after imaging under 365 nm excitation, and (f) photoluminescence photographs of 5a (powder), 5b, 5c, and 5e (absorbed paper).

[0044] The mechanically induced chromism is shown in Figure 4(a). The paper absorbed with the twisted form of 5a was heated to 60°C to induce a conformational change, resulting in the fabrication of paper absorbed with the bent form of 5a. An iron rod was then used to draw on the paper.

[0045] Vapor-induced chromism is shown in Figure 4(b). When a green drawing is placed in a closed container filled with DCM vapor at 25 °C, the drawing gradually disappears within 3 min. This is presumably due to the color change caused by microcrystallization induced by the solvent vapor.

[0046] The color change from green to yellow is also induced by thermally induced chromism. When a drawing is placed on a hot plate at 70°C, the drawing disappears in 20 seconds, as shown in Figure 4(c). The fluorenylidene-acridan derivative of this example is stabilized in its bent form by introducing an electron-donating group into the fluorene moiety or an electron-withdrawing group into the acridan moiety, so that the fluorenylidene-acridan derivative that has changed from a bent form to a twisted form by mechanochromism can be easily restored to the bent form by heat.

[0047] We investigated the robustness of the repeated drawing and erasing and confirmed that it could be repeated at least 50 times. 1 H NMR showed no evidence of any undesired reactions. These properties can be used to provide environmentally friendly printing materials that can be printed by applying pressure without the use of ink and that can be erased by heat. This phenomenon is believed to be explained by recrystallization into a folded form at temperatures above the glass transition temperature (approximately 70°C). As shown in Figure 4(c), differential scanning calorimetry (DSC) of 5a shows a broad endothermic peak near this temperature, which is consistent with this explanation. In the compounds of the other examples, this endothermic peak is seen in the range of 67°C to 75°C.

[0048] Adding DCM to the yellow powder produces a bluish-green solution, as shown in Figure 4(d). This color change is due to the formation of an equilibrium between the bent and twisted forms in the DCM solution. The yellow powder also shows a green color change upon dissolution. When the paper was placed on a hot plate at approximately 210 °C, melting was observed. This corresponds to the endothermic peak at approximately 210 °C in the DSC.

[0049] The fluorenylidene-acridan derivatives also exhibit luminescent piezochromism. By introducing a substituent into the fluorene moiety, the band of the photoluminescence spectrum was tuned over a wide range of 60 nm. The photoluminescence of 5a-c and 5e under excitation at 365 nm is shown in Figure 4(f). Even at low pressure, only very weak emission was observed after pressure application, as shown in Figure 4(e). This phenomenon is believed to be due to the conformational change from the luminescent bent type to the non-luminescent twisted type due to the application of pressure and the energy transition from the bent type to the twisted type. Before pressure application, there is an assembly of the bent type, but a small amount of twisted type is formed and dissociated from the assembly of the bent type upon pressure application. The energy gap of the twisted type is smaller than that of the bent type, and it does not emit light due to partial charge transfer. As a result, the small amount of twisted type functions to quench the fluorescence in the luminescent piezochromism. These properties make fluorenylidene-acridan derivatives promising materials for organic light-emitting piezochromism.

[0050] [Effects of Substituents and Solvents] Figure 5 shows the UV spectra of the fluorenylidene-acridan derivatives: Figure 5(a) shows the normalized absorption spectrum of the fluorenylidene-acridan derivatives in DCM, Figure 5(b) shows the normalized absorption spectrum of 5c in different solvents, Figure 5(c) shows the normalized absorption spectrum of 5e in different solvents, and Figure 5(d) shows the absorption spectrum of the same concentration of 5c in different ratios of DCM / glacial acetic acid and 5c in different ratios of DCM / glacial acetic acid.

[0051] To investigate the effect of the substituents on the equilibrium constant between the bent and twisted forms of 5a-f in DCM solution, UV-Vis absorption spectra were measured. The absorption peak of the charge transfer band was adjusted over a wide range from 620 nm to 750 nm by introducing six types of substituents into the fluorene moiety. A red shift was observed in 5f compared to 5a and 5c. This red shift is considered to be due to the increased charge transfer from the acridan moiety to the fluorene moiety due to the nitro group, which is a very strong electron-withdrawing group. 5a and 5c have two electron-donating groups at the 3,6- and 2,7-positions of the fluorene moiety, respectively, and their charge transfer bands are shifted to the short wavelength side (630-640 nm). The UV-Vis absorption of 5a-f in the range of 300-400 nm is quite different from each other, reflecting the presence of the substituents at the fluorene moiety. For example, 5e having a thienyl group and 5f having a nitro group contain lone pairs of S and O atoms, respectively, so that n→π * It exhibits a characteristic absorption around 300-350 nm due to the transition of

[0052] A wide range of solvent polarity parameter values ​​(E T Nine solvents with (30) values ​​ranging from 31.0 to 55.4 were selected, and the relationship between the solvent polarity and the absorption ratio of the bent and twisted conformations was analyzed. T A positive correlation was observed between the ratio of the absorption bands at around 670 nm and 430 nm. This suggests that the equilibrium shifts from the bent form to the twisted form as the polarity of the solvent increases. Furthermore, it was revealed that a red shift occurs as the polarity of the solvent increases. Methanol is an exception, but this is thought to be due to the effect of aggregation and the effect of equilibrium between the fluorenylidene-acridan derivative and the methanol adduct. Both the increase in absorbance and the red shift of the twisted form absorption band provide solvatochromism induced by the conformational transformation. Fluorenylidene-acridan derivatives are also expected to be used as new solvatochromic dyes by utilizing this color change.

[0053] As can be seen in Figure 5(d), 5c becomes protonated as the acidity of the solvent increases. Figure 6 shows the protonation of fluorenylidene-acridan derivatives. Figure 6(a) shows the nucleophilicity of 5a and the mechanism of protonation by acetic acid, and Figure 6(b) shows the electrophilicity of 5a and the mechanism of addition of methanol. A partially zwitterionic twisted fluorenylidene-acridan derivative is formed by deformation from the crowded structure accompanied by charge transfer from the acridan to the fluorene moiety. When the fluorenylidene-acridan derivative molecule is surrounded by polar acetic acid, the intramolecular charge transfer is further promoted, protonating the fluorene moiety and forming the bright yellow protonated 5a. This process is reversed by the addition of an organic base such as triethylamine.

[0054] The electrophilicity was also analyzed through the addition of methanol to the central double bond of 5a. The methanol adduct 6a is formed via the mechanism shown in Figure 6(b). The reaction is initiated by the attack of the lone pair of electrons of methanol on the slightly cationic acridan moiety. The fluorene moiety is then protonated. The X-ray structure of 6a is shown in Figure 8. The methanol adduct readily disappears back to 5a unless in the crystalline state.

[0055] [Electrochemical properties] 5a-e in DCM (Fc / Fc + Cyclic voltammograms at Fc / Fc (reference) showed reversible one-electron oxidation and one-electron reduction. The oxidation potentials of 5a-5e were Fc / Fc + The oxidation potentials ranged from -0.24 to -0.10 V relative to the reference. 5a showed the least negative oxidation potential, indicating that it is easier to oxidize compared to ferrocene due to the electron-donating methyl group of the fluorene moiety. Conversely, 5d showed a significantly higher oxidation potential (Fc / Fc) due to the electron-withdrawing bromo group of the fluorene moiety. + The reduction potential of 5a-e was Fc / Fc +The band gaps of the five compounds, 5d and 5e, which have bromo and thienyl groups, respectively, were 1.69 V (5d) and 1.87 V (5e), ​​which were smaller than the other compounds. The band gap of 5a (2.08 V) was the largest. Also, very small reductions of 5a-e were observed around -0.9 V, which was assigned to a bent-type reduction.

[0056] The charge carrier transport properties of the fluorenylidene-acridan derivatives were measured by the space-charge-limited current (SCLC) method. Hole and electron devices were fabricated with the configurations of ITO / PEDOT:PSS / fluorenylidene-acridan derivatives / MoO3 / Al and ITIO / ZnO / fluorenylidene-acridan derivatives / Al, respectively. The hole mobilities of 5a, 5c, 5d, and 5e are 6.6 × 10 -7 , 1.1×10 -7 , 1.1×10 -6 , and 6.3 × 10 -7 cm 2 V -1 s -1 The electron mobility of 5b could not be measured due to its high crystallinity. The electron mobilities of 5a, 5c, and 5d were 2.5×10 -8 , 1.4×10 -6 , and 7.7 × 10 -9 cm 2 V -1 s -1 These ambipolar transport properties are due to the contribution of the acridinium cation and fluorenyl anion, which act as positive and negative charge carriers, respectively. The above data show a good correlation between the electrical properties and the hole mobility. The hole mobility of the compounds with electron-withdrawing groups (bromo groups) was higher than that of the compounds with electron-donating groups (methyl, methoxy, and thienyl groups). This suggests that the increased charge transfer within the molecule stabilizes the twisted conformation, which increases the hole mobility. The improved charge carrier mobility obtained by the modification of the substituents can improve the properties of these semiconducting molecules.

[0057] [Dynamic stereochemistry and X-ray structure analysis] To understand the mechanism of the conformational transformation, we calculated the free energy difference between the bent and twisted conformers in the conformers of 5a and 5e and the two transition states. Since the substituents are symmetrically introduced at the fluorene moiety, the bent and twisted conformers are C S and C2 symmetry. Calculations were performed using the Gaussian09 package in B3LYP / 6-31G(d).

[0058] The free energy difference between the two conformations of 5a and 5e was calculated to be 2.8 and 5.7 kJ / mol, respectively. This indicates that the twisted conformation is more thermodynamically stable than the bent conformation in the B3LYP calculation. However, the difference in free energy between the conformations is small and can be considered to be almost the same energy.

[0059] Figure 7 shows the free energy diagrams of fluorenylidene-acridan derivatives. The relative rotation of the aromatic ring around C9=C9' for the conformational transformation between the bent and twisted forms is the main conformational transformation process. In 5e, the energy barrier between the minimum of the bent form and the minimum of the twisted form was low at 26.1 kJ / mol, indicating that the transformation between these two conformations can occur easily. The energy barrier for the transformation between the two minima of the twisted form was 42.8 kJ / mol.

[0060] Next, for both bent and twisted conformations, the distribution of molecular orbitals, the energy levels of HOMO-1, HOMO, LUMO, and LUMO+1, and the band gap (E gThe molecular orbital distributions (=HOMO-LUMO) were calculated. In the analysis of the distribution of molecular orbitals, no clear spatial separation of the HOMO and LUMO was observed except in a few cases. The bent forms of 5c and 5e were exceptions, in which the HOMO was located at the fluorene site due to the electron-donating methoxy and thienyl groups. Another exception was 5d, in which the LUMO was located mainly at the fluorene site in both the bent and twisted forms due to the strong electron-withdrawing nitro group. It was confirmed that the introduction of substituents into the fluorenylidene-acridan derivatives had the effect of significantly changing the distribution of molecular orbitals. Furthermore, the HOMO-LUMO transitions were observed to be due to the intramolecular charge transfer and π-π * It was concluded that the oxidative stress could contribute to both the oxidative stress and the transition.

[0061] [Table 1] As shown in Table 1, the twisted form has a higher HOMO level of -5.54 to -4.73 eV and a lower LUMO level of -2.04 to -2.73 eV compared to the bent form, and has a smaller band gap than the bent form. The twisted form 5f has the smallest band gap Eg and the deepest HOMO and LUMO of the six compounds. In 5f, the LUMO is distributed over the nitro group.

[0062] Figure 8 shows the single crystal X-ray structures of the fluorenylidene-acridan derivatives. As shown in Figure 8, the structures of the fluorenylidene-acridan derivatives other than 5f were determined by single crystal X-ray diffraction. For 5a and 5e, both bent and twisted conformers were obtained. Surprisingly, for 5a, the bent and twisted conformers existed in a 1:1 ratio in one unit cell. This is the first example of a bistricyclic aromatic ene (BAE) containing both conformers in one crystal. The structure of the methanol adduct 6a was also determined.

[0063] There are two known ways to alleviate steric hindrance in the crowded BAE fjord region: one is kinks and the other is bends. [Table 2]

[0064] The twisting results in a torsion angle ω. As shown in Table 2, the two sites on either side of the central double bond are twisted from ω=40° to 57°. For the twisted 5e, ω is as high as 56.7°, indicating a significant deformation from the planar ethylene structure.

[0065] The bends result in two types of dihedral angles. One is the dihedral angle in the fluorene moiety (AC) and the acridan moiety (DF), and the other is the dihedral angle between the fluorene moiety and the acridan moiety (ABC-DER). In the bend forms of 5c and 5e, the dihedral angles between D and F are 46.06° and 45.49°, respectively. Also, the bend angles of AC are generally larger than those of DF. This suggests that the bend of the acridan moiety contributes more to the relaxation of steric hindrance with larger bends. This also means that the planar fluorene moiety is rather rigid. The bend of the acridan moiety further relaxes the steric hindrance of the fjord region.

[0066] In the bent form, the bond length between C9 and C9' is 1.352 Å to 1.369 Å, which is slightly longer than the typical C=C bond length (1.34 Å). In contrast, in the staggered form, the bond length between C9 and C9' is 1.397 Å to 1.414 Å. Partial intramolecular charge transfer from the acridan moiety to the fluorene moiety is thought to lengthen the C9=C9' bond.

[0067] To analyze the fjord region of the fluorenylidene-acridan derivatives, the bent form of 5e was chosen. The distances between the non-bonded atoms in the fjord region are C1…C1' (3.000 Å), C8…C8' (3.055 Å), C1…H1' (2.318 Å), C8…H8' (2.216 Å), and H8…H8' (2.306 Å), suggesting penetrations of 14.0%, 12.1%, 23.8%, 4.1%, and 24.3% (the van der Waals radii of the carbon and hydrogen atoms are 1.71 Å and 1.15 Å, respectively).

[0068] The crystallinity of the fluorenylidene-acridan derivatives of this example is generally high. This is believed to be due to the stronger dipole-dipole interaction between molecules due to the introduction of a substituent at the fluorene moiety. The crystallinity of the bent type is generally higher than that of the twisted type, as shown by the change in color from a bluish green twisted type to a yellow bent type when the powder of the fluorenylidene-acridan derivative obtained after evaporating the solvent is further dried. This may be explained by the crystal packing force between the rigid structures of the bent type. The fluorenylidene-acridan derivatives of this example stabilize the bent type by introducing an electron donating group at the fluorene moiety or an electron withdrawing group at the acridan moiety, so that the crystallinity of the bent type can be further improved. The higher crystallinity of the bent type than that of the twisted type is the basis for the mechanochromic behavior of the fluorenylidene-acridan derivatives. Fluorenylidene-acridan derivatives can be used as smart materials in pressure, thermal, and other types of sensors.

[0069] The present disclosure has been described above based on examples. These examples are merely illustrative, and it will be understood by those skilled in the art that various modifications are possible in the combination of each component and each treatment process, and that such modifications are also within the scope of the present disclosure.

Claims

1. Formula (1) 【Chemistry 1】 (Here, R １ ~R １６ is a hydrogen atom, an alkyl group, a heteroalkyl group, an alkenyl group, a heteroalkenyl group, an alkynyl group, a heteroalkynyl group, a cycloalkyl group, a heterocycloalkyl group, an aryl group, a heteroaryl group, an alkoxy group, a carboxy group, a cyano group, a hydroxyl group, a thiol group, an amino group, a nitro group, or a halogen; at least one of R 1 to R 8 is an electron-donating group selected from the group consisting of an alkyl group, a thienyl group, an amino group, a hydroxyl group, and an alkoxy group; R １７ is an alkyl group, a heteroalkyl group, an alkenyl group, a heteroalkenyl group, an alkynyl group, a heteroalkynyl group, a cycloalkyl group, a heterocycloalkyl group, an alkoxy group, a carbonyl group, a carboxy group, a cyano group, a hydroxyl group, a thiol group, an amino group, an imino group, a nitro group, a halogen, or an aromatic ring group that is unsubstituted or has one or more substituents.

2. R ９ ~R １７ 2. The fluorenylidene-acridan derivative according to claim 1, wherein at least one of the above is an electron-withdrawing group selected from the group consisting of a carboxy group, a nitro group, and a halogen.

3. A method for producing the fluorenylidene-acridan derivative according to claim 1 or 2, comprising the steps of: Introducing an organic group into the acridone or fluorene; a cross-coupling reaction of acridone with fluorene to produce a fluorenylidene-acridan derivative of formula (1); A method for providing the above.

4. The step of producing the fluorenylidene-acridan derivative comprises: converting the acridone to a thioacridone; diazotizing the fluorene; reacting a thioacridone with a diazofluorene to produce a fluorenylidene-acridan derivative of formula (1); 4. The method of claim 3, comprising:

5. A mechanochromic material comprising the fluorenylidene-acridan derivative according to claim 1 or 2.

6. A charge transport material comprising the fluorenylidene-acridan derivative according to claim 1 or 2.

7. An electronic device comprising the mechanochromic material according to claim 5 or the charge transport material according to claim 6.

Images